Abstract
Out-band radiation is a severe problem for Cognitive Radio with OFDM system (CR-OFDM) which is caused by the sidelobe of OFDM signals. Lots of studies have been done on suppressing the sidelobe power and numerous methods have been proposed. In this paper, we propose a novel method to minimize the sidelobe by adding extended data carrier so called EDC to the original data carriers so as to protect primary user (PU) spectrum. Unlike the methods before, the EDCs are deployed within the secondary user (SU) data frequency spectrum to fully use the spectrum. Moreover, we derive the linear least squares problem to get the optimal weighting factors of EDCs to minimize the sidelobe power which is subject to an original data interference constraint. By simulation, we find that EDC is more capable in sidelobe suppression than method of Cancellation Carrier (CC) while EDC has only a small loss in BER performance.
Highlights
The wireless spectrum has been a scarce resource with the development of wireless communication
Out-band radiation is a severe problem for Cognitive Radio with OFDM system (CR-OFDM) which is caused by the sidelobe of OFDM signals
We assume a secondary user of CR-OFDM system with NS=10 subcarriers and a N=64 FFT applied for OFDM modulation
Summary
The wireless spectrum has been a scarce resource with the development of wireless communication. We will turn off some subcarriers at both ends of SU’s spectral bands to create a Guard Band to protect PU’s transmission from SU’s sidelobe interference [3] This method does not fully use the spectrum resources and its ability of sidelobe suppression is so limited. Key point of CC is to insert some subcarriers to the Guard Band located at both ends of the used OFDM spectrum They are not designed to transmit data but used to carry complex weighted factors to offset the sidelobe power of transmitted data signals which will create a clean and clear spectrum notch at the PU’s spectrum. With the EDC method, we will deploy the extended data carriers over the whole used OFDM spectrum and over the Guard Band.
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